1. Field of the Invention
The present invention generally relates to an acoustic signal processing unit for use with a sound equipment such as a Karaoke device which is an apparatus that radiates through a loudspeaker a piece of music as an accompaniment for a song reproduced from a recording medium and the singer's vocal when the singer sings toward a microphone to the accompaniment, an audio reverberation effecting device and so on, and more particularly to an acoustic signal processing unit such as a sound echo machine which is capable of generating a sound field similar to that of an auditorium such as a concert hall or the like, and also a new type of sound effecter which is capable of generating a unique sound effect that could not be obtained by a conventional sound effecter.
2. Description of the Prior Art
Hitherto, various sound echo machines have been provided as an acoustic signal processing unit, wherein an acoustic signal is repetitively fed back each time with a delay of 50 msec for generating a variety of tone qualities. FIG. 4 is a block diagram showing one example of a conventionally used sound echo machine, wherein reference numeral 1 denotes an input terminal, numeral 2 denotes an output terminal, 3 denotes an adder, 4 a delay circuit and numeral 5 denotes an attenuator.
With this construction above, an acoustic signal input through the input terminal 1 is output by way of the adder 3, wherein a part of the input signal is also fed to the attenuator 5 by way of the delay circuit 4 and the signal thus attenuated therein is further fed to the adder 3. The waveform of the signal output from this sound echo machine becomes an echo sound having a simple waveform repeated with a delay time t as shown in FIG. 5. In the figure, P0 is a basic waveform, and P1, P2 . . . are all fed back sounds each corresponding to a reflected sound.
On the other hand, in a conventional sound effecter also used as one of the acoustic signal processing units, it has been common to obtain a desired sound effect by use of only one acoustic signal processing section, and thus what is obtained thereby is only one type of sound effect. In order to solve this, there has also been provided a rather expensive sound effecter wherein a plurality of acoustic signal processing circuits each conducting different signal processing are connected either in series or in parallel, so that a plurality of different processing are conducted with respect to the input acoustic signal.
In recent years, there has been a demand for a sound echo machine as an acoustic signal processing unit used in a sound equipment such as the Karaoke device, which is capable of generating a sound field similar to that of a concert hall or the like, or specific sound effects corresponding to various types of music.
However, in the conventional echo machine having a delay circuit as shown in FIG. 4, an output waveform is determined simply by a delay time t generated at the delay circuit 4 and a single attenuation level at the attenuator 5 as is obvious by FIG. 5. In other words, the sound echo machine constructed as shown in FIG. 4 can not generate a substantial sound field as described above, but can produce only a simple echo sound without a variation of sound tone, and due to this fact, a sound echo machine capable of generating a further variation of fed back sounds and tone quality has been strongly desired.
In addition to this fact, in a sound effecter being used conventionally, a plurality of acoustic signal processing circuits are connected to conduct a plurality of sound processings, and the signal finally output thereby is only a total sum of a plurality of differently processed acoustic signal, which has not been sufficient for generating a satisfactory sound effect. Besides, in accordance with an improvement in technology of digital sound, a Digital Signal Processor (hereinafter referred to only as "DSP") has gradually been adopted in various sound equipments, so that by adopting this DSP for the above acoustic signal processing section, various sound effects can be provided by a program from external devices. However, there has still been a limitation to the sound effect due to the limitation of hardware or the processing speed thereof.